In the field of plastic blends, there continues to be a need for improved processes for compounding plastic materials. For example there is a need to reduce the number of processing steps for producing a fabricated part. In the field of thermoplastic polyolefins, for example, it remains attractive to have an effective material system that reduces the dependency upon pre-fabricating compounding steps, particularly those that subject the starting materials to heat history, that require energy consumption for processing, or both. In particular, it would be attractive for the improved process to provide fabricated parts with similar consistency and quality as current processes, which often rely upon a pre-fabricating compounding step. Such an improved process may have advantages including one or more of, the ability to rapidly change the composition of the blend material, to reduce thermal degradation of the plastic by eliminating at least one compounding step, to reduce waste or to reduce overall processing cost. One particularly attractive approach to “at-press” compounding is disclosed in U.S. patent application Ser. Nos. 11/736,342 and 11/821,706, which are both hereby expressly incorporated by reference for all purposes. In such “at-press” compounding, it is possible to avoid steps of pre-compounding together at elevated temperatures individual polymeric ingredients, and particularly avoiding a step of pre-compounding one or more polyolefins with each other or with elastomeric material such as a thermoplastic polyolefin.
One potential difficulty encountered in efforts to compound at-press is the result of the tendency for some materials to segregate due to differences in particle size, density, elasticity, electrical conductivity or other properties. One or more of the materials may also form agglomerations. Another potential source of difficulty may consequentially occur if one or more of the materials interfere with the dosing mechanisms, such as by interfering with a valve that controls the feeding of that material into a hopper or mixer. Notwithstanding, the advances recently seen in the art, there continues to be a need for additional improved processes to avoid one or more of these considerations.
Examples from the literature addressing the processes in this field include published U.S. Pat. Nos. 3,797,707; 4,286,883; 5,559,099; 6,951,900; and 6,403,691; EP Patent No. 958118 B1; PCT Application No. WO1997021528 A1; Troxel, T. G., “Modeling and scale-up of tumble blenders for highly segregating materials”, AIChE Spring National Meeting, Conference Proceedings, Orlando, Fla., United States, Apr. 23-27, 2006; McGlinchey, D., et al, “Particle segregation in pneumatic conveying lines.”, IMechE Conference Transactions, 2000; and Tang, P., et al, “Methods for Minimizing Segregation: A Review”, Particulate Science and Technology, vol. 22, No. 4, 2004, pp. 321-337; all hereby incorporated by reference for all purposes: and U.S. Pat. No. 6,111,206.